system lockup: clean/cache_resolution race detected

When I was untarring a 27M file [1] on my DragonFly box[2], the command
hung at some point after a few hundreds files were untarred. And the
following kernel messages got spit out on the screen:
Warning: vnode 0xd2b4dd38 clean/cache_resolution race detected
[diagnostic] cache_lock: blocked on 0xd40e9cd0 "Root"
I used the following command:
# cd /usr
# tar zxvf ~/tmp/pkgsrc.tar.gz
The system was not locked up and I could still do things on it. But when
I cd'ed into /usr/pkgsrc/CVS and do a `ls', the command just hung on me
again. At this time `ls' on other directories like /etc /usr etc was
still ok though. Then I did a `find /usr/ports | wc -l' and this time
the system got totally locked up [3].
I paniced the system and managed to have the core files generated, but I
don't have a place to put it. So let me know if anybody would like to
take a look at the core.
[1] The file can be downloaded from:
ftp://ftp.netbsd.org/pub/NetBSD/packages/pkgsrc.tar.gz),
[2] I am running -CURRENT and the source was checked out on 03/08/2005.
[3] The problem is easy to producable: just untar pkgsrc.tar.gz again
and do a `find /usr/ports | wc -l'.
-Rongsheng